Phosphorus–Chlorophyll Relationships under Contrasting Herbivory and Thermal Stratification: Predictions and Patterns

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Abstract
Analyses of the relationships between total phosphorus (TP) and chlorophyll a (Chl) among a large number of temperate lake ecosystems having contrasting herbivore communities and thermal stratification reveal that systems lacking large Daphnia (SH systems) exhibit four times more Chl yields than systems having large Daphnia (LH systems) in oligotrophic as well as eutrophic and hypereutrophic systems. Mixed (MIX) systems exhibit greater Chl yields than stratified (STR) systems. Within each group of stratified and mixed systems, greater Chl yields to constant TP are observed in systems lacking large Daphnia (MIX-SH and STR-SH) than those having large Daphnia (MIX-LH and STR-LH). Consequently, a hierarchy of Chl yield patterns is produced; STR-LH and MIX-SH systems exhibit the lowest and highest Chl yields, respectively, at constant TP. These patterns may be a reflection of variable chemical (nutrients), biological (herbivory), and physical (thermal stratification) characteristics among aquatic ecosystems. Sigmoid patterns of TP–Chl relationships appear to be related to the transition from stratified to mixed systems along the TP gradient. The finding that highly variable Chl yields to TP can be summarized into a set of TP–Chl trajectories for specific types of lake ecosystems may have strong implications for lake management.